Mode detection for DVB receiver

ABSTRACT

Systems, apparatus and methods are provided for detecting the mode of a received OFDM signal. A received signal may be correlated with one or more time-delayed version of itself resulting in a set of correlation signals. Each correlation signal may be analyzed for one or more characteristics that can be used to determine the symbol length of the received signal. In order to minimize the number of correlations performed, one or more correlations can be used with varying symbol lengths and a fixed guard interval length. The correlation signals can be processed by filters, and the characteristics of the filtered correlation signals can be analyzed to determine the guard interval length of the received signal. In addition to detecting symbol length, the present invention can be used to detect receiver impairment and perform any appropriate compensations.

This application claims the benefit of U.S. Provisional Application No.60/823,215 filed Aug. 22, 2006, the disclosure of which is incorporatedherein by reference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to the field of orthogonal frequency-divisionmultiplexing (OFDM) and, more particularly, to mode detection of OFDMsignals.

In OFDM systems such as digital video broadcast (DVB) systems, eachsymbol has a predetermined length and is transmitted as part of atransmission block. In order to counteract multi-path distortions(reflected signals that are received after the primary signal isreceived), most systems incorporate a redundant portion into eachtransmission block. This redundant portion is generally known as a guardinterval and is usually expressed as a fraction of the symbol length.

Some OFDM receivers are capable of receiving different types of OFDMsignals. In order to properly demodulate a received signal, such adevice must be able to identify what mode (symbol length and guardinterval size) was used to generate the signal. For example, if a deviceis designed to receive OFDM signals with a symbol length of 2048, 4096or 8192 samples and a guard interval that is ¼, ⅛, 1/16 or 1/32 of eachsymbol length, there are 12 different combinations of parameters (ormodes) that the device must be able to recognize. Traditionally, OFDMreceivers perform a different correlation for each mode, and thecorrelation having the maximum peak amplitude will be used to identifythe appropriate mode. However, this approach is computationallyintensive and may sometimes fail to identify the correct mode.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of ordinary skill in the art,through comparison of such systems with some aspects of the presentinvention as set forth in the remainder of the present application withreference to the drawings.

SUMMARY OF THE INVENTION

In accordance with the principles of the present invention, systems,apparatus and methods are provided for computationally efficientdetection of the mode of a received OFDM signal.

A received signal may be correlated with one or more delayed versions ofitself resulting in a set of correlation signals. The amount of delayand the summation interval of each correlation operation may correspondto a possible symbol length, adjustment length (e.g., to compensate forreceiver impairment), and/or guard interval size. Each correlationsignal may be evaluated based on one or more characteristics that may beused to determine the strongest correlation and, therefore, the mostlikely symbol length and guard interval size of the received signal.

In order to minimize the number of correlations performed, one or morepreliminary correlations may be performed to test for varying symbollengths and a fixed guard interval size. The characteristics of thesepreliminary correlation signals may be analyzed to determine the symbollength of the received signal. The preliminary correlation signals maybe processed by filters that may be dependant on the determined symbollength. The characteristics of the filtered correlation signals may beanalyzed to determine the guard interval size of the received signal.

The preliminary correlation may also be down-sampled before filtering.The down-sampling may be at a rate that is predetermined (e.g., based onone or more hardware requirements) or a rate that varies according tothe determined symbol length. If the down-sampling rate is dependentupon the determined symbol length, it may not be necessary for thesubsequent filters to reconfigure themselves based on the determinedsymbol length.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will be apparent uponconsideration of the following detailed description, taken inconjunction with the accompanying drawings, in which like referencecharacters refer to like parts throughout, and in which:

FIG. 1 is a simplified block diagram of a conventional OFDM transmitter;

FIG. 2 is a simplified timing diagram of conventional OFDM signals withdifferent guard intervals;

FIG. 3 is a simplified block diagram of an OFDM system in accordancewith an embodiment of the present invention;

FIG. 4 is a simplified block diagram of mode detection circuitry inaccordance with an embodiment of the present invention;

FIG. 5 is a simplified block diagram of mode detection circuitry inaccordance with another embodiment of the present invention;

FIG. 6 is a simplified block diagram of mode detection circuitry inaccordance with yet another embodiment of the present invention;

FIG. 7 is a flowchart of a mode detection method in accordance with anembodiment of the present invention;

FIG. 8 is a flowchart of a mode detection method in accordance withanother embodiment of the present invention;

FIG. 9A is a block diagram of an exemplary hard disk drive that canemploy the disclosed technology;

FIG. 9B is a block diagram of an exemplary digital versatile disc thatcan employ the disclosed technology;

FIG. 9C is a block diagram of an exemplary high definition televisionthat can employ the disclosed technology;

FIG. 9D is a block diagram of an exemplary vehicle that can employ thedisclosed technology;

FIG. 9E is a block diagram of an exemplary cell phone that can employthe disclosed technology;

FIG. 9F is a block diagram of an exemplary set top box that can employthe disclosed technology; and

FIG. 9G is a block diagram of an exemplary media player that can employthe disclosed technology.

DETAILED DESCRIPTION OF THE INVENTION

In order to generate OFDM signals, sequential bits of binary data areconverted to temporal signals for transmission. FIG. 1 shows a typicalOFDM transmitter 100. Transmitter 100 may include at leastserial-to-parallel circuitry 110, binary conversion circuitry 120, IFFTcircuitry 130, guard interval (GI) insertion circuitry 140, RF front endcircuitry 150 and an antenna 160. Serial-to-parallel circuitry 110 canconvert serial bits of a predetermined size to parallel data lines.Binary conversion circuitry 120 can map combinations of binary bits ontoa sub carrier frequency for transmission. Each frequency may be coupledwith an input of IFFT circuitry 130. IFFT circuitry 130 may have Ninputs 131 and can calculate the Inverse Discrete Fourier Transform ofthe N frequencies in order to produce an output sequence (or symbol) ofN samples. In some embodiments, data may not be assigned to every inputof IFFT circuitry 130 (i.e., only select carrier frequencies may beused).

The outputs of IFFT circuitry 130 may be coupled with guard intervalinsertion circuitry 140 which may use portion 141 of samples from theend of the sequence to insert portion 142 at the beginning of thesequence. The size of the added portion may be defined as a fraction,referred to as the guard interval size (M_(r)), of the original symbollength N. For example, in the case where the are eight samples in asymbol (N=8) and the guard interval is a quarter of the symbol length(M_(r)=¼), the last two samples of the symbol will be copied andinserted before the symbol as a guard interval. Guard intervals andtheir purpose are discussed in more detail below and in connection withFIG. 2.

After the guard interval is added, the lengthened transmission block canbe processed by RF front end circuitry 150. Front end circuitry 150 canconvert the sequence to a signal acceptable for transmission. Front endcircuitry 150 can broadcast the converted signal through antenna 160.

There are interference issues which may affect wirelessly transmitteddata. For example, wireless signals might reflect off of objects (e.g.,large buildings) and arrive at a receiver after the primary signal.These delayed signals, called multipath distortions, can interfere withsubsequent signals causing transmission errors. In order to preventmultipath distortions, many OFDM systems transmit a guard interval.Typically represented as a fraction of the symbol length, a guardinterval is a copy of a portion of the symbol. In order to create guardintervals, most systems copy a portion from the end of a symbol andattach it to the beginning of the symbol. This redundant portion in thebeginning of each symbol is designed to prevent any late-arrivingreflections of previous symbols and early-arriving reflections of nextsymbols from interfering with the data in the current symbol.

FIG. 2 shows multiple OFDM signals with guard intervals of differentsizes. For example, signal 2100 includes a guard interval 2110 that is1/32 (M_(r)= 1/32) the size of symbol length 2120. Signal 2100 maytherefore require a total transmission block length 2130 which may be33/32 the size of symbol length 2120. The waveform transmitted duringguard interval 2110 may be the same as the waveform 2122 transmitted atthe end of the symbol. Signals 2200, 2300 and 2400 each include guardintervals that are different fractions of symbol length 2120. Inparticular, signals 2200, 2300 and 2400 may include respective guardintervals 2210, 2310 and 2410 which may each be 1/16, ⅛ and ¼ of symbollength 2120. It is understood that while the guard intervals shown inFIG. 2, as well as those in the systems and methods discussed below aredescribed as having a size that is ¼, ⅛, 1/16 and 1/32 of theirassociated symbols, guard intervals of different sizes can be usedwithout deviating from the spirit of the present invention.

While the term guard interval size (M_(r)) is used to reference afraction of symbol length (e.g., ¼, ⅛, 1/16, 1/32, etc.), the term guardinterval length (M) can be used herein to identify the actual length ofa guard interval. For example, if a symbol length is 1024 samples, aguard interval size of ⅛ (i.e., M_(r)=⅛) corresponds to a guard intervallength of 128 samples (i.e., M=128). In this example, a totaltransmission block would include 1152 samples.

FIG. 3 shows OFDM system 3000 which may include transmitter 100 andreceiver 3200. Transmitter 100 is analogous to transmitter 100 shown anddescribed in connection with FIG. 1. Transmitter 100 may include anantenna 160 in order to transmit signals. Receiver 3200 may include atleast an antenna 3250, RF circuitry 3240, mode detection circuitry 3290,guard interval (GI) removal circuitry 3230, FFT circuitry 3220 andfrequency data 3210. Antenna 3250 may receive RF signals. Antenna 3250may be configured to receive signals of frequencies which areappropriate for the electronics housed in receiver 3200. For example,antenna 3250 may receive a bandwidth of frequencies which may cover theareas of the spectrum around the frequencies of one or more carrierwaves that may be transmitted by transmitter 100. RF circuitry 3240 maydemodulate the received radio waves in order to separate the signal fromthe carrier waves. Additionally, RF circuitry 3240 may convert thesignal into digital values. {tilde over (y)}(n) can represent thedigital signals which correspond to the radio waves received by antenna3250.

Receiver 3200 may receive signals from different transmitters, dependingon, for example, the location of the receiver. Each transmitter might beconfigured to generate signals in a different way (e.g., using differentmodes). For example, different transmitters might use IFFT circuitry ofvarying sizes and insert guard intervals of different lengths. In orderto properly receive the various modes of signals, mode detectioncircuitry 3290 may detect the symbol length (N) and the guard intervallength (M) used to generate the symbols received from input 3292. Modedetection circuitry 3290 can communicate these signal parameters (M andN) to the guard interval removal circuitry 3230 via output 3294 and toFFT circuitry 3220 via output 3296. Guard interval removal circuitry3230 and FFT circuitry 3220 may use the parameters (M and N) forextracting data from the received signal {tilde over (y)}(n). It isunderstood that mode detection circuitry 3290 may transmit guardinterval size (M_(r)) instead of (or in addition to) guard intervallength (M).

Mode detection circuitry 3290 may determine the symbol length (N) andthe guard interval length (M) of the transmitted signal by employing anynumber of techniques described below. For example, mode detectioncircuitry may implement one or more correlation algorithms on a receivedsignal. By analyzing the outputs of the correlations, mode detectioncircuitry 3290 may determine the symbol length (N) and the guardinterval length (M) of the signal. An exemplary correlation algorithmmay be performed in accordance with:

$\begin{matrix}{{r_{i,j}(n)} = {\sum\limits_{l = 0}^{L - 1}\;{{\overset{\sim}{y}\left( {n + l} \right)}{\overset{\sim}{y}\left( {n + i + l} \right)}}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$whereL=i×j  Equation 2where the received signal ({tilde over (y)}(n)) may be compared with ashifted version of itself ({tilde over (y)}(n+i)) over an interval(L=i×j) of samples. In the situation where the above correlation isapplied to a received signal, i may represent a possible symbol length(N), and j may represent a possible guard interval size (M_(r)) that wasused to generate the symbol.

For example, a symbol may be generated with a symbol length of 2048samples (N=2048), and a guard interval that is ¼ of the symbol length(M_(r)=¼) may be inserted before the symbol. In this situation, themaximum amplitude of r_(2048,1/4)(n) may be high because the relativedelay of the correlated signals (i) is equal to the symbol length (N) ofthe received signal, and the summation interval (L=i×j) is equal to thelength of the guard interval (M=N×M_(r)). Therefore, if i and j arechosen correctly, at the point (n) where the portion of the earliersignal ({tilde over (y)}(n)) is the guard interval, the portion of thedelayed signal (y(n+i)) will be the portion of the symbol that wascopied to create the guard interval. Accordingly, a high correlationvalue will be generated.

FIG. 4 shows an embodiment of mode detection circuitry 3290 inaccordance with the principles of the present invention. Mode detectioncircuitry 3290 may include at least length detection circuitry 4000;selector circuitry 4500; symbol filters 4610, 4620, 4630 and 4640;characteristic extraction circuitry 4710, 4720, 4730 and 4740; decisioncircuitry 4800; an input 3292; and outputs 3294 and 3296.

Length detection circuitry 4000 may be configured to assume a guardinterval (e.g., j₁) in order to determine the correct symbol length (N)of a received signal. After the correct symbol length (N) is determined,other parts of mode detection circuitry 3290 may be used to correctlydetermine the guard interval size (M_(r)) using the previouslydetermined symbol length (N). For example, a correlated signal fromlength detection circuitry 4000 may be filtered according to thedetected symbol length (N) to remove unnecessary data (e.g., correlationdata that is not related to the guard interval of a received signal).The filtered correlation signal may then be used to determine the guardinterval size (M_(r)) or guard interval length (M).

Length detection circuitry 4000 may include correlators 4110, 4120 and4130; characteristic extraction circuitry 4210, 4220 and 4230; filters4310, 4320 and 4330; and decision circuitry 4400. Correlators 4110, 4120and 4130 may be configured to correlate input 3292 with a delayedversion of itself in accordance with Equations 1 and 2. It is understoodthat although only three correlators 4110, 4120 and 4130 are drawn, anynumber of correlators may be used to detect the symbol length (N) of thereceived signal. It is also understood that one correlation unit maygenerate the same correlation signals as correlators 4110, 4120 and4130. Such a central correlation unit may be able to simplifyimplementation by, for example, sharing circuitry related to commonfunctions across all three correlators 4110, 4120 and 4130.

Each of correlators 4110, 4120 and 4130 can be configured to use thesame possible guard interval size (e.g., j₁) and different possiblesymbol lengths (e.g., i₁, i₂, i₃). This can allow length detectioncircuitry 4000 to compute which i value is the actual value of thereceived signal's symbol length (N).

Possible guard interval size j₁ may be chosen so that it is smaller thanany of the other possible guard interval sizes. This is because thesmaller guard interval size will result in a smaller summation interval(L=i×j) which can fit within the larger guard intervals and stillgenerate a strong correlation signal.

An example of a possible configuration of correlators 4110, 4120 and4130 would be to set the parameters in accordance with:

$\begin{matrix}{j_{1} = \frac{1}{32}} & {{Equation}\mspace{14mu} 3}\end{matrix}$i₁=2048  Equation 4i₂=4096  Equation 5i₃=8192  Equation 6Where j₁ may be the smallest possible guard interval size. In thisscenario, the receiver will be able to detect which possible symbollength out of i₁, i₂ and i₃ was the actual symbol length (N) used togenerate the received signal. The correlation outputs can be processedthrough characteristic extraction circuitry 4210, 4220 and 4230 whichcan measure characteristics (e.g. ratio of peak amplitude to averageamplitude, number of peaks, maximum peak amplitude, etc.) of thecorrelation signals. The outputs of characteristic extraction circuitry4210, 4220 and 4230 can be sent through filters 4310, 4320 and 4330.

Filters 4310, 4320 and 4330 may filter characteristic data so thatdecision circuitry 4400 can more efficiently compare the characteristicsof the three correlation signals r_(i) ₁ _(,j) ₁ (n), r_(i) ₂ _(,j) ₁(n) and r_(i) ₃ _(,j) ₁ (n). For example, filters 4310, 4320 and 4330can remove any falsely detected characteristics and scale thecharacteristic data. This may allow the data from each correlationsignal to be easily compared.

Decision circuitry 4400 can compare the characteristic data of thedifferent correlation signals in order to determine which signal has thestrongest correlation. Decision circuitry 4400 may apply a weightedfunction to one or more characteristics of the correlation signal. Forexample, decision circuitry 4400 may designate the correlation signalwith the highest ratio of peak amplitude to average amplitude and thelowest peak count as being the signal with the strongest correlation.Decision circuitry 4400 can output the symbol length (N) whichcorresponds to the strongest correlation signal. For example, decisioncircuitry 4400 can output the value of i₂ if the correlation signal fromcorrelator 4120 has characteristics which indicate that it is thestrongest of the three correlation signals.

Output 3294 can be coupled to any other circuitry that might benefitfrom knowing the symbol length of the received signal. For example,output 3294 can be coupled to FFT circuitry (see circuitry 3220 in FIG.3) which can configure itself according to the detected symbol length(N). Length detection circuitry 4000 may connect the correlation signalsfrom correlators 4110, 4120 and 4130 with outputs 4112, 4122 and 4132.These signals may be used by other parts of mode detection circuitry3290 in order to simplify computations. For example, other portions ofmode detection circuitry 3290 may be electrically coupled with outputs4112, 4122, and 4132 such that they do not have to recorrelate thereceived signal.

Mode detection circuitry 3290 can also detect the guard interval of areceived signal. By using the symbol length (N) determined by decisioncircuitry 4400, mode detection circuitry 3290 can filter one or more ofthe signals from correlators 4110, 4120 and 4130 according to possibleguard interval sizes (e.g., j₁, j₂, j₃, j₄) and the previously detectedsymbol length (N).

Selector circuitry 4500 can route an appropriate correlation signal(e.g., according to determined symbol length N) to symbol filters 4610,4620, 4630 and 4640. It is understood that although only four symbolfilters 4610, 4620, 4630 and 4640 are shown, any number of filters maybe used to detect the guard interval size of the received signal.

Symbol filters 4610, 4620, 4630 and 4640 may be filters designed toevaluate the correlation signal from selector circuitry 4500 accordingto different guard interval sizes. For example, symbol filter 4610 maycorrespond to a first possible guard interval size (j₁), symbol filter4620 may correspond to a second possible guard interval size (j₂),symbol filter 4630 may correspond to a third possible guard intervalsize (j₃) and symbol filter 4640 may correspond to a fourth possibleguard interval size (j₄). The outputs of symbol filters 4610, 4620, 4630and 4640 can be computed in accordance with:

$\begin{matrix}{{{\overset{\sim}{r}}_{N,j}(n)} = {\sum\limits_{v = 0}^{V - 1}\;{{{r_{N,j_{1}}(n)}}{h\left( {{v\left( {N\left( {1 + j} \right)} \right)} - n} \right)}}}} & {{Equation}\mspace{14mu} 7}\end{matrix}$In the above equation, N can represent the symbol length determined bylength detection circuitry 4000, and N(1+j) can represent a possiblecombined symbol and guard interval length. The value of N(1+j) can setthe spacing between the samples of the correlation signal r_(N,j) ₁ (n)that are evaluated by each symbol filter. If N and j are selectedcorrectly, the value of N(1+j) will be the total length of one symboland guard interval. According to Equation 7, if the value of j whichdoesn't correspond to the actual guard interval size (M_(r)) is usedthen the output of the symbol filter may have low values because thesymbol filter has evaluated samples of the correlation signal with lowvalues. These low values may indicate that the corresponding portions ofthe received signal are not highly correlated and, therefore, the symbolfilter used an improper value of j.

Alternatively, if the correct value of j is used then the samples of thecorrelation signal which the filter evaluates may consistently have highvalues which represent a strong correlation between the correspondingportions of the received signal.

In Equation 7, the value of V can be predetermined and can affect howmany correlation signal samples each symbol filter evaluates. It may beadvantageous to select a value of V which is large enough to properlydetermine if the correlation signal samples have a consistently highvalue. It may also be advantageous to select a value of V which is smallenough to not waste any unnecessary time or computational power. In someembodiments, each symbol filter can include a one-pole filter whichaverages two or more samples of the correlation signal. For example, ifV samples of a correlation signal are evaluated, the sum of the valuescan be divided by V to give an average correlation value. This averagevalue can be indicative of whether or not the value of j corresponds tothe correct guard interval size (M_(r)).

Symbol filters 4610, 4620, 4630 and 4640 may be coupled with output 3294of decision circuitry 4400. This output may provide symbol filters 4610,4620, 4630 and 4640 with the detected symbol length value (N) to usewhen evaluating correlation signals in accordance with Equation 7.

An example of a possible configuration of symbol filters 4610, 4620,4630 and 4640 would be to set the parameters as follows:

$\begin{matrix}{j_{1} = \frac{1}{32}} & {{Equation}\mspace{14mu} 8} \\{j_{2} = \frac{1}{16}} & {{Equation}\mspace{14mu} 9} \\{j_{3} = \frac{1}{8}} & {{Equation}\mspace{14mu} 10} \\{j_{4} = \frac{1}{4}} & {{Equation}\mspace{14mu} 11}\end{matrix}$The resulting filter outputs may each correspond to a different possibleguard interval size (M_(r)). The outputs of symbol filters 4610, 4620,4630 and 4640 can be coupled with characteristic extraction circuitry4710, 4720, 4730 and 4740 which can measure one or more characteristicsof the correlation signals.

Characteristic extraction circuitry 4710, 4720, 4730 and 4740 maymeasure the same or different characteristics as characteristicextraction circuitry 4210, 4220 and 4230. If characteristic extractioncircuitry 4710, 4720, 4730 and 4740 functions in a manner that issimilar to characteristic extraction circuitry 4210, 4220 and 4230, thenpart or all of characteristic extraction circuitry 4210, 4220 and 4230can be used in place of part or all of characteristic extractioncircuitry 4710, 4720, 4730 and 4740. Characteristic extraction circuitry4710, 4720, 4730 and 4740 can measure, for example, the ratio of peakamplitude to average amplitude, the number of peaks, or the average peakamplitude. Decision circuitry 4800 can output the guard interval length(M) or guard interval size (M_(r)) which corresponds to the strongestcorrelation signal. It is understood that once the symbol length (N) andguard interval size (M_(r)) are known, the guard interval length(M=N×M_(r)) can be easily computed for any of the embodiments discussedherein. Output 3296 can be coupled to any other circuitry that mightbenefit from knowing the guard interval size of the received signal. Forexample, output 3294 can be coupled to guard interval removal circuitry(e.g., circuitry 3230 in FIG. 3) which can configure itself in responseto the detected guard interval length (M) or guard interval size(M_(r)).

FIG. 5 shows an embodiment of mode detection circuitry 3290 inaccordance with the principles of the present invention. Mode detectioncircuitry 3290 can include length detection circuitry 4000; a selector5500; a decimator 5550; symbol filters 5610, 5620, 5630 and 5640;characteristic extraction circuitry 5710, 5720, 5730 and 5740; decisioncircuitry 5800; input 3292 and outputs 3294 and 3296. Length detectioncircuitry 4000 is analogous to length detection circuitry 4000 shown anddescribed in connection with FIG. 4. Length detection circuitry mayinclude correlators, characteristic extraction circuitry, filters anddecision circuitry (not shown) similar to the elements shown in lengthdetection circuitry 4000 of FIG. 4. The correlator signal outputs 4112,4122 and 4132 may be coupled with selector circuitry 4500 fordistribution to other parts of mode detector circuitry 3290.Additionally, the detected symbol length (N) output 3294 of lengthdetection circuitry 4000 can be coupled with selector 5500 and symbolfilters 5610, 5620, 5630 and 5640.

Selector 5500 can route the correlation signal which corresponds to thedetermined symbol length N to decimator 5550. Decimator 5550 maydown-sample the correlation signal by a predetermined rate (e.g., ¼, ½).For example, decimator 5550 may average every four samples to produceone output or may keep every fourth sample and disregard the rest. Thisdown-sampling may simplify the design and minimize the size of symbolfilters 5610, 5620, 5630 and 5640 as well as characteristic extractioncircuitry 5710, 5720, 5730 and 5740.

The output of decimator 5550 may be coupled with the inputs of symbolfilters 5610, 5620, 5630 and 5640. It is understood that although onlyfour symbol filters 5610, 5620, 5630 and 5640 are drawn, any number ofsymbol filters may be used to detect the guard interval of the receivedsignal.

Symbol filters 5610, 5620, 5630 and 5640 can be similar, respectively,to symbol filters 4610, 4620, 4630, and 4640 of FIG. 4. Accordingly,symbol filters 5610, 5620, 5630 and 5640 can implement Equation 7.However, symbol filters 5610, 5620, 5630 and 5640 may adjust thereceived value of N to compensate for the amount of down-sampling thatis performed by decimator 5550. For example, if length detectioncircuitry 4000 determines that the value of N is i₃, and decimator 5550down-samples the correlation signal by 4 samples, then symbol filters5610, 5620, 5630 and 5640 may use i₃/4 as the value of N.

Symbol filters 5610, 5620, 5630 and 5640 may output filtered correlationsignals {tilde over (r)}_(N,j) _(i) (n), {tilde over (r)}_(N,j) ₂ (n),{tilde over (r)}_(N,j) ₃ (n) and {tilde over (r)}_(N,j) ₄ (n) tocharacteristic extraction circuitry 5710, 5720, 5730 and 5740 which canmeasure one or more characteristics (e.g. ratio of peak amplitude toaverage amplitude, number of peaks, maximum peak amplitude, etc.) of thefiltered correlation signals. The outputs of characteristic extractioncircuitry 5710, 5720, 5730 and 5740 can be sent to decision circuitry5800. Decision circuitry 5800 may analyze the characteristic data foreach filtered correlation signal to determine the appropriate guardinterval length (M) or guard interval size (M_(r)). Decision circuitry5800 may apply a weighted function to one or more measuredcharacteristics of the filtered correlation signals. Decision circuitry5800 may, for example, output the guard interval length whichcorresponds to the filtered correlation signal with the highest ratio ofpeak amplitude to average amplitude, the most number of peaks above acertain threshold or the maximum peak amplitude. Output 3296 can becoupled to any other circuitry that may benefit from knowing the guardinterval size of the received signal. For example, output 3296 can becoupled to guard interval removal circuitry (e.g., circuitry 3230 ofFIG. 3) which can configure itself in response to the detected guardinterval length (M).

FIG. 6 shows an embodiment of mode detection circuitry 3290 inaccordance with the principles of the present invention. Mode detectioncircuitry 3290 can include length detection circuitry 4000;characteristic extraction circuitry 6710, 6720, 6730 and 6740; decisioncircuitry 6800; a selector 6500; a decimator 6550; symbol filters 6610,6620, 6630 and 6640; input 3292 and outputs 3294 and 3296.

Length detection circuitry 4000 may be configured to assume a guardinterval (e.g., j₁) in order to determine the correct symbol length (N)of a received signal. After the correct symbol length (N) is determined,the correlated signals from length detection circuitry 4000 may bedown-sampled according to the determined symbol length (N). Thisdown-sampled signal may then be filtered to determine the guard intervallength (M). If the correlation signals have been down-sampled to astandard size, the symbol filters 6610, 6620, 6630 and 6640 used toprocess the correlation data may not have to be adjusted to compensatefor the determined symbol length (N).

Length detection circuitry 4000 is analogous to length detectioncircuitry 4000 shown and described in connection with FIG. 4. Lengthdetection circuitry may include correlators, characteristic extractioncircuitry, filters and decision circuitry (not shown) similar to theelements shown in length detection circuitry 4000 of FIG. 4. Thecorrelator signal outputs 4112, 4122 and 4132 may be coupled withselector 6500 for distribution to other parts of mode detector circuitry3290. Additionally, the detected symbol length (N) output 3294 of lengthdetection circuitry 4000 can be coupled with selector 6500 and decimator6550. Selector 6500 can route the correlation signal which correspondsto the detected symbol length N to decimator 6550, and decimator 6550may down-sample the correlation signal by an amount that is dependantupon the detected symbol length N.

The amount of down-sampling may be chosen so that the period or lengthof the correlation signal at the decimator output is the same regardlessof the received signal's length. For example, if the value of symbollength N is determined to be 8192 samples, decimator 6550 maydown-sample the correlation signal by 8, and if the value of N isdetermined to 2048 samples, decimator 6550 may down-sample thecorrelation signal by 2. The output of decimator 6550 can be coupledwith the inputs of symbol filters 6610, 6620, 6630 and 6640 which canevaluate samples of the correlation signal which correspond to differentguard intervals.

Symbol filters 6610, 6620, 6630 and 6640 can function in a manner thatis similar to symbol filters 5610, 5620, 5630 and 5640 of mode detectioncircuitry 3290 in FIG. 5. However, the outputs of filters 6610, 6620,6630 and 6640 can be computed in accordance with:

$\begin{matrix}{{{\overset{\sim}{r}}_{N,u}(n)} = {\sum\limits_{v = 0}^{V - 1}\;{{_{N,j_{1}}(n)}{h\left( {{v\left( {G\left( {1 + u} \right)} \right)} - n} \right)}}}} & {{Equation}\mspace{14mu} 12}\end{matrix}$In the above equation, G can be chosen to correspond to the period orlength of the correlation signal that is output from decimator 6550.

Following the above example, if value of N is 8192 samples thendecimator 6550 may down-sample by 8; and if the value of N is 2048samples then decimator 6550 may down-sample by 2. In this example, G maybe chosen to be 1024 since that may be the standard period or length ofdown-sampled correlation signals. By changing the decimation scale inresponse to the determined symbol length N, the scaling factor G insymbol filters 6610, 6620, 6630 and 6640 may not need to be changedaccording to the value of N.

It is understood that although only four symbol filters 6610, 6620, 6630and 6640 are drawn, any number of filters may be used to detect theguard interval of the received signal. It is also understood that onefilter circuit can be used to filter all of the correlation signals.Such a filter circuit may be able to simplify implementation by, forexample, sharing circuitry related to functions common across filters6610, 6620 and 6630.

The examples shown above reference symbol lengths of 2048, 4096 and8192, and guard interval sizes of ¼, ⅛, 1/16 and 1/32. However, it isunderstood that other symbol lengths and guard interval sizes can beused without deviating from the spirit of the present invention.

FIG. 7 shows a flowchart of method 700 for detecting the mode of areceived OFDM signal in accordance with an embodiment of the presentinvention. At step 710, a plurality of time-delayed versions of thereceived signal may be received, wherein each one of the plurality oftime-delayed versions corresponds to a different potential symbol lengthof the received signal. At step 720, the symbol length of the receivedsignal may be detected by correlating the received signal with theplurality of time-delayed versions of the received signal to output aplurality of correlated signals. At step 730, one of the plurality ofcorrelated signal outputs may be selected corresponding to the detectedsymbol length. At step 740, the guard interval size of the receivedsignal may be detected by filtering the selected correlated signaloutput.

FIG. 8 shows a flowchart of method 800 for detecting the mode of areceived OFDM signal in accordance with another embodiment of thepresent invention. At step 810, the received signal may be correlatedwith first and second versions of the received signal to createrespective first and second correlation signals. At step 820, the firstand second correlation signals may be compared to detect the symbollength of the received signal. At step 830, one of the first and secondcorrelation signals may be filtered to create a plurality of filteredcorrelation signals, wherein the one of the first and second correlationsignals corresponds with the detected symbol length of the receivedsignal. At step 840, the plurality of filtered correlation signals maybe compared to detect the guard interval size of the received signal.

Referring now to FIGS. 9A-9G, various exemplary implementations of thepresent invention are shown.

Referring now to FIG. 9A, the present invention can be implemented in ahard disk drive 900. The present invention may implement either or bothsignal processing and/or control circuits, which are generallyidentified in FIG. 9A at 902. In some implementations, the signalprocessing and/or control circuit 902 and/or other circuits (not shown)in the HDD 900 may process data, perform coding and/or encryption,and/or perform calculations, and/or format data that is output to and/orreceived from a magnetic storage medium 906.

The HDD 900 may communicate with a host device (not shown) such as acomputer, mobile computing devices such as personal digital assistants,cellular phones, media or MP3 players and the like, and/or other devicesvia one or more wired or wireless communication links 908. The HDD 900may be connected to memory 909 such as random access memory (RAM),nonvolatile memory such as flash memory, read only memory (ROM) and/orother suitable electronic data storage.

Referring now to FIG. 9B, the present invention can be implemented in adigital versatile disc (DVD) drive 910. The present invention mayimplement either or both signal processing and/or control circuits,which are generally identified in FIG. 9B at 912, and/or mass datastorage of the DVD drive 910. The signal processing and/or controlcircuit 912 and/or other circuits (not shown) in the DVD drive 910 mayprocess data, perform coding and/or encryption, perform calculations,and/or format data that is read from and/or data written to an opticalstorage medium 916. In some implementations, the signal processingand/or control circuit 912 and/or other circuits (not shown) in the DVDdrive 910 can also perform other functions such as encoding and/ordecoding and/or any other signal processing functions associated with aDVD drive.

The DVD drive 910 may communicate with an output device (not shown) suchas a computer, television or other device via one or more wired orwireless communication links 917. The DVD drive 910 may communicate withmass data storage 918 that stores data in a nonvolatile manner. The massdata storage 918 may include a hard disk drive (HDD). The HDD may havethe configuration shown in FIG. 9A. The HDD may be a mini HDD thatincludes one or more platters having a diameter that is smaller thanapproximately 1.8″. The DVD drive 910 may be connected to memory 919such as RAM, ROM, nonvolatile memory such as flash memory and/or othersuitable electronic data storage.

Referring now to FIG. 9C, the present invention can be implemented in ahigh definition television (HDTV) 920. The present invention mayimplement either or both signal processing and/or control circuits,which are generally identified in FIG. 9C at 922, a WLAN interface 929and/or mass data storage 927 of the HDTV 920. The HDTV 920 receives HDTVinput signals in either a wired or wireless format and generates HDTVoutput signals for a display 926. In some implementations, signalprocessing circuit and/or control circuit 922 and/or other circuits (notshown) of the HDTV 920 may process data, perform coding and/orencryption, and/or perform calculations, format data and/or perform anyother type of HDTV processing that may be required.

The HDTV 920 may communicate with mass data storage 927 that stores datain a nonvolatile manner such as optical and/or magnetic storage devices.At least one HDD may have the configuration shown in FIG. 9A and/or atleast one DVD may have the configuration shown in FIG. 9B. The HDD maybe a mini HDD that includes one or more platters having a diameter thatis smaller than approximately 1.8″. The HDTV 920 may be connected tomemory 928 such as RAM, ROM, nonvolatile memory such as flash memoryand/or other suitable electronic data storage. The HDTV 920 also maysupport connections with a WLAN via a WLAN network interface 929.

Referring now to FIG. 9D, the present invention implements a controlsystem of a vehicle 930, a WLAN interface 948 and/or mass data storage946 of the vehicle control system. In some implementations, the presentinvention may implement a powertrain control system 932 that receivesinputs from one or more sensors such as temperature sensors, pressuresensors, rotational sensors, airflow sensors and/or any other suitablesensors and/or that generates one or more output control signals such asengine operating parameters, transmission operating parameters, and/orother control signals.

The present invention may also be implemented in other control systems940 of the vehicle 930. The control system 940 may likewise receivesignals from input sensors 942 and/or output control signals to one ormore output devices 944. In some implementations, the control system 940may be part of an anti-lock braking system (ABS), a navigation system, atelematics system, a vehicle telematics system, a lane departure system,an adaptive cruise control system, a vehicle entertainment system suchas a stereo, DVD, compact disc and the like. Still other implementationsare contemplated.

The powertrain control system 932 may communicate with mass data storage946 that stores data in a nonvolatile manner. The mass data storage 946may include optical and/or magnetic storage devices for example harddisk drives HDD and/or DVDs. At least one HDD may have the configurationshown in FIG. 9A and/or at least one DVD may have the configurationshown in FIG. 9B. The HDD may be a mini HDD that includes one or moreplatters having a diameter that is smaller than approximately 1.8″. Thepowertrain control system 932 may be connected to memory 947 such asRAM, ROM, nonvolatile memory such as flash memory and/or other suitableelectronic data storage. The powertrain control system 932 also maysupport connections with a WLAN via a WLAN network interface 948. Thecontrol system 940 may also include mass data storage, memory and/or aWLAN interface (all not shown).

Referring now to FIG. 9E, the present invention can be implemented in acellular phone 950 that may include a cellular antenna 951. The presentinvention may implement either or both signal processing and/or controlcircuits, which are generally identified in FIG. 9E at 952, a WLANinterface 968 and/or mass data storage 964 of the cellular phone 950. Insome implementations, the cellular phone 950 includes a microphone 956,an audio output 958 such as a speaker and/or audio output jack, adisplay 960 and/or user input 962 such as a keypad, pointing device,voice actuation and/or other input device. The signal processing and/orcontrol circuits 952 and/or other circuits (not shown) in the cellularphone 950 may process data, perform coding and/or encryption, and/orperform calculations, format data and/or perform other cellular phonefunctions.

The cellular phone 950 may communicate with mass data storage 964 thatstores data in a nonvolatile manner such as optical and/or magneticstorage devices for example hard disk drives HDD and/or DVDs. At leastone HDD may have the configuration shown in FIG. 9A and/or at least oneDVD may have the configuration shown in FIG. 9B. The HDD may be a miniHDD that includes one or more platters having a diameter that is smallerthan approximately 1.8″. The cellular phone 950 may be connected tomemory 966 such as RAM, ROM, nonvolatile memory such as flash memoryand/or other suitable electronic data storage. The cellular phone 950also may support connections with a WLAN via a WLAN network interface968.

Referring now to FIG. 9F, the present invention can be implemented in aset top box 980. The present invention may implement either or bothsignal processing and/or control circuits, which are generallyidentified in FIG. 9F at 984, a WLAN interface 996 and/or mass datastorage 990 of the set top box 980. The set top box 980 receives signalsfrom a source such as a broadband source and outputs standard and/orhigh definition audio/video signals suitable for a display 988 such as atelevision and/or monitor and/or other video and/or audio outputdevices. The signal processing and/or control circuits 984 and/or othercircuits (not shown) of the set top box 980 may process data, performcoding and/or encryption, and/or perform calculations, format dataand/or perform any other set top box function.

The set top box 980 may communicate with mass data storage 990 thatstores data in a nonvolatile manner. The mass data storage 990 mayinclude optical and/or magnetic storage devices for example hard diskdrives HDD and/or DVDs. At least one HDD may have the configurationshown in FIG. 9A and/or at least one DVD may have the configurationshown in FIG. 9B. The HDD may be a mini HDD that includes one or moreplatters having a diameter that is smaller than approximately 1.8″. Theset top box 980 may be connected to memory 994 such as RAM, ROM,nonvolatile memory such as flash memory and/or other suitable electronicdata storage. The set top box 980 also may support connections with aWLAN via a WLAN network interface 996.

Referring now to FIG. 9G, the present invention can be implemented in amedia player 1000. The present invention may implement either or bothsignal processing and/or control circuits, which are generallyidentified in FIG. 9G at 1004, a WLAN interface 1016 and/or mass datastorage 1010 of the media player 1000. In some implementations, themedia player 1000 includes a display 1007 and/or a user input 1008 suchas a keypad, touchpad and the like. In some implementations, the mediaplayer 1000 may employ a graphical user interface (GUI) that typicallyemploys menus, drop down menus, icons and/or a point-and-click interfacevia the display 1007 and/or user input 1008. The media player 1000further includes an audio output 1009 such as a speaker and/or audiooutput jack. The signal processing and/or control circuits 1004 and/orother circuits (not shown) of the media player 1000 may process data,perform coding and/or encryption, and/or perform calculations, formatdata and/or perform any other media player function.

The media player 1000 may communicate with mass data storage 1010 thatstores data such as compressed audio and/or video content in anonvolatile manner. In some implementations, the compressed audio filesinclude files that are compliant with MP3 format or other suitablecompressed audio and/or video formats. The mass data storage may includeoptical and/or magnetic storage devices for example hard disk drives HDDand/or DVDs. At least one HDD may have the configuration shown in FIG.9A and/or at least one DVD may have the configuration shown in FIG. 9B.The HDD may be a mini HDD that includes one or more platters having adiameter that is smaller than approximately 1.8″. The media player 1000may be connected to memory 1014 such as RAM, ROM, nonvolatile memorysuch as flash memory and/or other suitable electronic data storage. Themedia player 1000 also may support connections with a WLAN via a WLANnetwork interface 1016.

It is understood that the foregoing is only illustrative of theprinciples of the invention, and that the invention can be practiced byother than the described embodiments and aspects of the invention, whichare presented for purposes of illustration and not of limitation, andthe present invention is limited only by the claims which follow.

1. A method for detecting a symbol length and guard interval length of areceived signal, the method comprising: receiving, with a receiver, aplurality of time-delayed versions of the received signal, wherein eachone of the plurality of time-delayed versions corresponds to a differentpotential symbol length of the received signal and each time-delayedversion corresponds to the received signal delayed by a predeterminedtime interval; determining the symbol length of the received signal bycorrelating, using correlation circuitry, the received signal with theplurality of time-delayed versions of the received signal to output aplurality of correlated signals and a control signal identifying thedetermined symbol length; receiving, with selection circuitry, thecontrol signal and each one of the plurality of correlated signaloutputs; and selecting, using the selection circuitry, one of thereceived plurality of correlated signal outputs based upon the receivedcontrol signal.
 2. The method of claim 1, further comprising: detectingthe guard interval length of the received signal by filtering theselected correlated signal output.
 3. The method of claim 1, wherein thedetecting the symbol length of the received signal comprises:determining one or more characteristics of each of the plurality ofcorrelated signals; and comparing the determined characteristics of eachone of the plurality of correlated signals with another one of theplurality of correlated signals.
 4. The method of claim 3 wherein thecharacteristics comprise: ratios of peak to average amplitude of each ofthe plurality of correlated signals; and count values of a number ofpeaks of each of the plurality of correlated signals.
 5. The method ofclaim 2, further comprising down-sampling the selected correlated signaloutput before the detecting the guard interval length.
 6. The method ofclaim 5, wherein the down-sampling is dependant on the detected symbollength of the received signal.
 7. The method of claim 2, wherein thefiltering comprises using a plurality of filters to output a pluralityof correlated and filtered signals.
 8. The method of claim 7, whereineach one of the plurality of filters corresponds to a different guardinterval length.
 9. The method of claim 8, wherein detecting the guardinterval length of the received signal comprises comparing the pluralityof correlated and filtered signals.
 10. A system for detecting a symbollength and guard interval length of a received signal, the systemcomprising: symbol length detection circuitry operable to: receive aplurality of time-delayed versions of the received signal, wherein eachone of the plurality of time-delayed versions corresponds to a differentpotential symbol length of the received signal and each time-delayedversion corresponds to the received signal delayed by a predeterminedtime interval; determine the symbol length of the received signal bycorrelating the received signal with the plurality of time-delayedversions; and output a plurality of correlated signals and a controlsignal identifying the determined symbol length; and selector circuitryoperable to: receive the control signal and each one of the plurality ofcorrelated signal outputs; and select one of the received plurality ofcorrelated signal outputs based upon the received control signal. 11.The system of claim 10, further comprising: filter circuitry operable tofilter the selected correlated signal output and generate correlated andfiltered signal output; and decision circuitry operable to detect theguard interval length of the received signal by analyzing the correlatedand filtered signal output.
 12. The system of claim 10, wherein thesymbol length detection circuitry is operable to: determine one or morecharacteristics of each one of the plurality of correlated signals; andcompare the determined characteristics of each one of the plurality ofcorrelated signals with another one of the plurality of correlatedsignals.
 13. The system of claim 12, wherein the characteristicscomprise: ratios of peak to average amplitude of each of the pluralityof correlated signals; and count values of a number of peaks of each ofthe plurality of correlated signals.
 14. The system of claim 11, furthercomprising: a decimator operable to: down-sample the selected correlatedsignal output; and provide the down-sampled correlated signal output tothe filter circuitry.
 15. The system of claim 14, wherein the decimatoris operable to down-sample the selected correlated signal outputaccording to a down-sampling factor that is dependant on the detectedsymbol length of the received signal.
 16. The system of claim 11,further comprising guard interval length detection circuitry thatincludes a plurality of filters that are coupled with the selectorcircuitry and are operable to output a plurality of correlated andfiltered signals.
 17. The system of claim 16, wherein each one of theplurality of filters corresponds to a different guard interval length.18. The system of claim 17, wherein the decision circuitry is operableto compare the plurality of correlated and filtered signals.
 19. Anapparatus for detecting a symbol length and guard interval length of areceived signal, the apparatus comprising: means for receiving aplurality of time-delayed versions of the received signal, wherein eachone of the plurality of time-delayed versions corresponds to a differentpotential symbol length of the received signal, wherein eachtime-delayed version corresponds to the received signal delayed by apredetermined time interval; means for determining the symbol length ofthe received signal by correlating the received signal with theplurality of time-delayed versions of the received signal to output aplurality of correlated signals and a control signal identifying thedetermined symbol length; means for receiving the control signal andeach one of the plurality of correlated signal outputs; and means forselecting one of received the plurality of correlated signal outputsbased upon the received control signal.
 20. The apparatus of claim 19,further comprising: means for detecting the guard interval length of thereceived signal by filtering the selected correlated signal output. 21.The apparatus of claim 19, wherein the means for detecting the symbollength of the received signal comprises: means for determining one ormore characteristics means of each of the plurality of correlatedsignals; and means for comparing the determined characteristics means ofeach one of the plurality of correlated signals with another one of theplurality of correlated signals.
 22. The apparatus of claim 21, whereinthe characteristics means comprise: ratios means of peak to averageamplitude of each of the plurality of correlated signals; and countvalues means of a number of peaks of each of the plurality of correlatedsignals.
 23. The apparatus of claim 20, further comprising means fordown-sampling the selected correlated signal output before the means fordetecting the guard interval length.
 24. The apparatus of claim 23,wherein the down-sampling means has a factor that is dependant on thedetected symbol length of the received signal.
 25. The apparatus ofclaim 20, wherein the means for filtering comprises using a plurality offilter means to output a plurality of correlated and filtered signals.26. The apparatus of claim 25, wherein each one of the plurality offilter means corresponds to a different guard interval length.
 27. Theapparatus of claim 26, wherein the means for detecting the guardinterval length of the received signal comprises means for comparing theplurality of correlated and filtered signals.
 28. A method for detectinga symbol length and guard interval length of a received signal, themethod comprising: correlating, using correlation circuitry, thereceived signal with first and second versions of the received signal tocreate respective first and second correlation signals; comparing thefirst and second correlation signals to determine the symbol length ofthe received signal; receiving, with selection circuitry, (1) a controlsignal identifying the determined symbol length and (2) each one of thefirst and second correlation signals; selecting, using the selectioncircuitry, one of the received first and second correlation signalsbased upon the received control signal; and filtering, using filtercircuitry, the selected one of the first and second correlation signalsto create a plurality of filtered correlation signals.
 29. The method ofclaim 28, further comprising: comparing the plurality of filteredcorrelation signals to detect the guard interval length of the receivedsignal.
 30. The method of claim 28, wherein the guard interval length ofthe received signal comprises a copy of another portion of the receivedsignal.
 31. The method of claim 28, wherein the first and secondversions of the received signal are delayed with respect to the receivedsignal by a predetermined time interval.
 32. The method of claim 31,wherein the respective predetermined time interval of the first andsecond versions of the received signal corresponds to a predeterminedsymbol length of the received signal.
 33. The method of claim 28,wherein the received signal is correlated with the first and secondversions of the received signal over a summation interval.
 34. Themethod of claim 33 wherein the summation interval of each correlationcorresponds to a possible symbol length of the received signal and apossible guard interval length of the received signal.
 35. The method ofclaim 28, wherein comparing the first and second correlation signals todetect the symbol length of the received signal comprises: generating aset of characteristic data based on one or more characteristics of thefirst and second correlation signals; and analyzing the set ofcharacteristic data to determine the symbol length of the receivedsignal.
 36. The method of claim 35, wherein the set of characteristicdata comprises: ratios of peak to average amplitude of each correlationsignal; and count values of a number of peaks of each correlationsignal.
 37. The method of claim 36, wherein the analyzing the set ofcharacteristic data to determine the symbol length of the receivedsignal comprises: choosing a symbol length which corresponds to acorrelation signal that has the highest ratio of peak to averageamplitude and the lowest count value of a number of peaks.
 38. Themethod of claim 29, wherein comparing the filtered correlation signalsto detect the guard interval length of the received signal comprises:generating a set of characteristic data based on one or morecharacteristics of the filtered correlation signals; and analyzing theset of characteristic data to determine the guard interval length of thereceived signal.
 39. The method of claim 38, wherein the set ofcharacteristic data comprises: ratios of peak to average amplitude ofeach filtered correlation signal.
 40. The method of claim 39, whereinthe analyzing the set of characteristic data to determine the guardinterval length of the received signal comprises: choosing a guardinterval length which corresponds to a filtered correlation signal thathas the highest ratio of peak to average amplitude.
 41. A system fordetecting a symbol length and guard interval length of a receivedsignal, the system comprising: a plurality of correlators operable to:correlate the received signal with first and second versions of thereceived signal; and output respective first and second correlationsignals; first decision circuitry operable to: compare the first andsecond correlation signals; determine the symbol length of the receivedsignal; and output a control signal identifying the determined symbollength; and selection circuitry operable to: receive the control signaland each one of the first and second correlation signals; and select oneof the received first and second correlation signals based upon thereceived control signal.
 42. The system of claim 41, further comprising:filter circuitry operable to: filter one of the first and secondcorrelation signals, wherein the one of the first and second correlationsignals corresponds to the detected symbol length of the receivedsignal; and output a plurality of filtered correlation signals; andsecond decision circuitry operable to: compare the plurality of filteredcorrelation signals; and detect the guard interval length of thereceived signal.
 43. The system of claim 41, wherein the guard intervalof the received signal comprises a copy of another portion of thereceived signal.
 44. The system of claim 41, wherein the plurality ofcorrelators delay the first and second versions of the received signalby a predetermined time interval.
 45. The system of claim 44, whereinthe predetermined time interval is different for the first and secondversions of the received signal.
 46. The system of claim 45, wherein therespective predetermined time interval of the first and second versionsof the received signal corresponds to a predetermined symbol length ofthe received signal.
 47. The system of claim 41, wherein the pluralityof correlators are operable to correlate the received signal with thefirst and second versions of the received signal over a summationinterval.
 48. The system of claim 47 wherein each one of the pluralityof correlators have a summation interval that corresponds to a possiblesymbol length of the received signal and a possible guard intervallength of the received signal.
 49. The system of claim 41, wherein thefirst decision circuitry is operable to: generate a set ofcharacteristic data based on one or more characteristics of the firstand second correlation signals; analyze the set of characteristic data;and determine the symbol length of the received signal.
 50. The systemof claim 49, wherein the set of characteristic data comprises: ratios ofpeak to average amplitude of each correlation signal; and count valuesof a number of peaks of each correlation signal.
 51. The system of claim50, wherein the first decision circuitry is operable to: choose a symbollength which corresponds to a correlation signal that has the highestratio of peak to average amplitude and the lowest count value of anumber of peaks.
 52. The system of claim 42, wherein the second decisioncircuitry is operable to: generate a set of characteristic data based onone or more characteristics of the filtered correlation signals; analyzethe set of characteristic data; and determine the guard interval lengthof the received signal.
 53. The system of claim 52, wherein the set ofcharacteristic data comprises: ratios of peak to average amplitude ofeach filtered correlation signal.
 54. The system of claim 53, whereinthe second decision circuitry is operable to: choose a guard intervallength which corresponds to a filtered correlation signal that has thehighest ratio of peak to average amplitude.
 55. An apparatus fordetecting a symbol length and guard interval length of a receivedsignal, the apparatus comprising: means for correlating the receivedsignal with first and second versions of the received signal to createrespective first and second correlation signals; means for comparing thefirst and second correlation signals to detect determine the symbollength of the received signal and output a control signal identifyingthe determined symbol length; means for receiving the control signal andeach one of the first and second correlation signals; means forselecting one of the received first and second correlation signals basedupon the received control signal; means for filtering the selected oneof the first and second correlation signals to create a plurality offiltered correlation signals.
 56. The apparatus of claim 55, furthercomprising: means for comparing the plurality of filtered correlationsignals to detect the guard interval length of the received signal. 57.The apparatus of claim 55, wherein the guard interval of the receivedsignal comprises a copy of another portion of the received signal. 58.The apparatus of claim 55, wherein the correlating means delays thefirst and second versions of the received signal by a predetermined timeinterval.
 59. The apparatus of claim 58, wherein the predetermined timeinterval is different for the first and second versions of the receivedsignal.
 60. The apparatus of claim 59, wherein the respectivepredetermined time interval of the first and second versions of thereceived signal corresponds to a predetermined symbol length of thereceived signal.
 61. The apparatus of claim 55, wherein the receivedsignal is correlated with the first and second versions of the receivedsignal over a summation interval.
 62. The apparatus of claim 61 whereinthe summation interval of each correlation corresponds to a possiblesymbol length of the received signal and a possible guard intervallength of the received signal.
 63. The apparatus of claim 55, whereinmeans for comparing the first and second correlation signals to detectthe symbol length of the received signal comprises: means for generatinga set of characteristic data means based on one or more characteristicsmeans of the first and second correlation signals; and means foranalyzing the set of characteristic data means to determine the symbollength of the received signal.
 64. The apparatus of claim 63, whereinthe set of characteristic data means comprises: ratios means of peak toaverage amplitude of each correlation signal; and count values means ofa number of peaks of each correlation signal.
 65. The apparatus of claim64, wherein the means for analyzing the set of characteristic data todetermine the symbol length of the received signal comprises: means forchoosing a symbol length which corresponds to a correlation signal thathas the highest ratio means of peak to average amplitude and the lowestcount value means of a number of peaks.
 66. The apparatus of claim 56,wherein means for comparing the filtered correlation signals to detectthe guard interval length of the received signal comprises: means forgenerating a set of characteristic data means based on one or morecharacteristics means of the filtered correlation signals; and means foranalyzing the set of characteristic data to determine the guard intervallength of the received signal.
 67. The apparatus of claim 66, whereinthe set of characteristic data means comprises: ratios means of peak toaverage amplitude of each filtered correlation signal.
 68. The apparatusof claim 67, wherein the means for analyzing the set of characteristicdata means to determine the guard interval length of the received signalcomprises: means for choosing a guard interval length which correspondsto a filtered correlation signal that has the highest ratio means ofpeak to average amplitude.
 69. A system for detecting a symbol lengthand guard interval length of a received signal, the system comprising: aplurality of correlators, wherein each correlator is operable to:correlate the received signal with a time-delayed version of thereceived signal, wherein the time-delayed version corresponds to thereceived signal delayed by a predetermined time interval, and output acorrelated signal; first decision circuitry coupled to the plurality ofcorrelators and operable to: determine the symbol length from thecorrelated signals, and output a control signal identifying thedetermined symbol length; and selector circuitry coupled to theplurality of correlators and operable to: receive the control signal andthe correlated signal from each one of the plurality of correlators; andselect one of the correlated signals received from the plurality ofcorrelators based upon the received control signal.
 70. The system ofclaim 69, further comprising: a plurality of filters coupled to theselector circuitry and operable to filter the selected correlatedsignal; second decision circuitry coupled to the plurality of filtersand operable to determine the guard interval length from the filteredand correlated signals.
 71. The system of claim 69 further comprisingdecimator circuitry operable to down-sample the output of the selectorcircuitry.
 72. A system for detecting a symbol length and guard intervallength of a received signal, the system comprising: symbol lengthdetection circuitry operable to: determine the symbol length of thereceived signal; and output a control signal identifying the determinedsymbol length; a plurality of correlators operable to correlate thereceived signal with time-delayed versions of the received signal tooutput a plurality of correlated signals, wherein the time-delayedversion corresponds to the received signal delayed by a predeterminedtime interval; selection circuitry operable to: receive the controlsignal and each one of the plurality of correlated signal outputs; andselect one of the received plurality of correlated signal outputs basedupon the received control signal; filters operable to filter theselected one of the correlated signals to output a correlated andfiltered signal; and decision circuitry operable to determine the guardinterval length of the received signal based on the correlated andfiltered output signal.
 73. The system of claim 72 further comprisingdecimator circuitry operable to down-sample the output of thecorrelators.